The present invention relates to ammonia for use in the manufacture of a GaN-type compound semiconductor and a method for producing a GaN-type compound semiconductor using the ammonia.
FIG. 3 shows an example of conventional GaN-type compound semiconductor devices. The GaN-type compound semiconductor device shown here has a constitution such that a buffer layer 2 comprising GaxAl1-xN (wherein 0xe2x89xa6xxe2x89xa61) which is a GaN-type compound, a Si-doped n-type GaxAl1-xN layer (n-type clad layer) 3 which is an n-type clad layer doped with Si, a Zn-doped GaxAl1-xN layer (active layer) 4 which is a light emitting active layer doped with Zn, and a Mg-doped p-type GaxAl1-xN layer (p-type clad layer) 5 which is a p-type clad layer doped with Mg are laminated in sequence on a sapphire substrate 1 and electrodes 6 and 7 are provided on the n-type clad layer 3 and p-type clad layer 5, respectively.
This GaN-type compound semiconductor device can be used as a blue light emitting diode.
FIGS. 1 and 2 show an example of a production apparatus for use in the manufacture of the above-described GaN-type compound semiconductor device.
The production apparatus shown here is a metal-organic chemical vapor deposition (MOCVD) reactor and comprises a reaction chamber 11 for housing a sapphire substrate, a support part 12 for holding the sapphire substrate in the reaction chamber 11, a heater 13 for heating the sapphire substrate supported by the support part 12, organic metal containers 14 and 15 as supply sources of organic metals, organic metal gas inlet tubes 16 and 17 for introducing organic metal gases supplied from the containers 14 and 15 into the reaction chamber 11, an ammonia charging container 18 as a supply source of ammonia gas, an ammonia gas inlet tube 19 for introducing the ammonia gas supplied from the charging container 18 into the reaction chamber 11, an outlet tube 20 for discharging gases out of the reaction chamber 11, a Si compound container 23, a Zn compound container 24, a Mg compound container 25, and inlet tubes 26, 27 and 28 for introducing the compounds supplied from the containers 23, 24 and 25 into the reaction chamber 11.
The epitaxial wafer for use in the manufacture of the GaN-type compound semiconductor device is manufactured using the above-described production apparatus according to the MOCVD process as described below.
In the production of the GaN-type compound semiconductor device, a sapphire substrate 1 is housed in a reactor 11, an organic gallium compound housed in a container 14 and an organic aluminum compound housed in a container 15 are bubbled with H2 gas using tubes 21 and 22, the organic gallium compound gas and organic aluminum compound gas obtained are introduced together with H2 gas into the reaction chamber 11 through inlet tubes 16 and 17, at the same time, ammonia gas supplied from a charging container 18 is introduced into the reaction chamber 11 through an inlet tube 19, and then a buffer layer 2 comprising GaxAl1-xN is formed on the surface of the sapphire substrate 1 using these organic gallium compound gas, organic aluminum gas and ammonia compound gas as raw materials.
Subsequently, a Si compound supplied from a container 23 is fed into the reaction chamber 11 through a tube 26 together with the above-described organic gallium compound, organic aluminum compound and ammonia gas to form an n-type clad layer 3 on the buffer layer 2.
Then, a Zn compound supplied from a container 24 is fed into the reaction chamber 11 through a tube 27 together with the above-described organic gallium compound, organic aluminum compound and ammonia gas to form an active layer 4 on the n-type clad layer 3.
Thereafter, a Mg compound supplied from a container 25 is fed into the reaction chamber 11 through a tube 28 together with the above-described organic gallium compound, organic aluminum compound and ammonia gas to form a p-type clad layer 5 on the active layer 4.
The thus-manufactured epitaxial wafer is removed from the reaction chamber 11 and electrodes 6 and 7 are provided on the n-type and p-type clad layers 3 and 5, respectively, thereby obtaining a GaN-type compound semiconductor device.
The above-described conventional technique is, however, disadvantageous in that the GaN-type compound semiconductor device obtained tends not to satisfy the light emitting property, particularly brightness. Accordingly, a technique capable of producing a GaN-type compound semiconductor device having excellent light emitting property without failure has been demanded.
The present invention has been made under these circumstances, and an object of the present invention is to provide a method for manufacturing a GaN-type compound semiconductor, where a GaN-type compound semiconductor having excellent light emitting property can be manufactured without fail.
The present inventors have found that the water concentration in the ammonia gas used as a raw material in the manufacture of GaN-type compound semiconductors has a great effect on the light emitting property such as brightness of the GaN-type compound semiconductor. The present invention has been accomplished based on this finding.
More specifically, the ammonia for use in the manufacture of a GaN-type compound semiconductor of the present invention is filled in a charging container such that at least a part of the ammonia is liquid, and the liquid phase ammonia has a water concentration determined by a Fourier-transform infrared spectroscopy (FT-IR) of 0.5 vol ppm or less.
Furthermore, the method for producing a GaN-type compound semiconductor of the present invention comprises introducing the above-described ammonia in the gaseous state into a reaction chamber housing therein a substrate, and forming a layer comprising a GaN-type compound using the ammonia on the substrate.